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Embedded libc

Embedded libc, a libc library adapted for embedded systems and bare metal environments.

Mlibc Features

• Low resource usage
• OpenSource
• Especially for RISC-V
• Clear and understandable code structure
• Scalable
• Highly portable

File Structure

mlibc File Structure

├───arch                -- Hardware-specific optimized implementations
├───crt                 -- Hardware-specific startup code
├───include             -- Header files
│   └───sys             -- System-related header files, typically included as <sys/head.h>
├───src                 -- Source files
│   ├───internal        -- Internal header files
│   ├───misc            -- Miscellaneous, contains modules that can be implemented in a single file
│   ├───stdio           -- Standard IO module
│   └───stdlib          -- Standard utility library module
├───helloworld          -- Helloworld testcase
│   └───qemu            -- qemu bare-metal config
│     └───qemu-device	-- Specific to the QEMU virtual machine device, related scripts and header files
├───mkconfigs           -- Scripts related to make
    └───qemu            -- qemu configuration

Background

Our Expectations

● mlibc can support multiple embedded toolchains, including gcc (arm/risc-v) and even LLVM compilers.

● Designed for low-resource systems, providing excellent support for embedded real-time operating systems (such as RT-Thread) and bare metal.

● Optimized for RISC-V 32/64, compatible with mainstream RISC-V MCUs.

● Uses make and scons for building.

● Reserve

Our Plans

● Use QEMU/RISC-V 32GC simulation to output the first "hello world" (completed).

● Add the basic crt.s, string, and printf functions for the bare-metal version of mlibc (completed).

● Improve mlibc based on this environment.

Quick Start

mlibc Library Compilation

Development Environment

For simple C library compilation, the development environment is relatively straightforward; make and the appropriate toolchain are sufficient.

make + toolchain

Compilation Steps

1. Configure the environment variables corresponding to the toolchain (Please refer to the detailed steps in the "QEMU-Bare Metal Development" section below)

Compile the C library

1. Navigate to the mlibc folder, open the command line, and use make to compile the static library.

# Here, we use the ARM architecture static library as an example
make mlibc ARCH=arm

2. A static library named libmlibc.a will be generated in the mlibc/build/arm directory. To integrate it with the toolchain, you can rename the file to libc.a for use.

Compile crt0

1. Navigate to the mlibc folder, open the command line, and use make to compile crt0.

# Here, we use the ARM architecture crt0 as an example
make crt0 ARCH=arm

2. The generated file will be located in mlibc/build/$(ARCH)/crtobj, named crt0.o.

Mlibc Development/Test Environment Setup

Running RT-Thread on QEMU

Development Environment

Tutorial for setting up the environment on Windows:

Note: The original RT-Thread documentation link is outdated. Please refer to the official RT-Thread website (https://www.rt-thread.org/) or repository (https://github.com/RT-Thread/rt-thread) for the latest documentation on setting up the development environment.

By following the official tutorials, you can run RT-Thread in a Windows environment.

vexpress-a9 + RT-Thread

Macro Configuration

Navigate to the rt-thread\bsp\qemu-vexpress-a9 folder, open env, and enter menuconfig in the command line to enter the configuration interface.

Switch DFS v2.0 to DFS v1.0:

• RT-Thread Components
  • DFS: device virtual file system
    • The version of DFS (DFS v1.0)

Download the mlibc package:

• RT-Thread online packages
  • system packages
    • Select the sixth option from the bottom: mlibc: Embedded libc, especially for RISC-V

After finishing the menuconfig, you need to download the mlibc package before compiling:

# Load the RT-Thread environment
. ~/.env/env.sh

# Update packages to download mlibc
pkgs --update

This will download mlibc to bsp/qemu-vexpress-a9/packages/mlibc-latest.

Then you can enter scons -j12 in the command line to compile.

Note: There are known compilation issues with vexpress-a9 + RT-Thread integration. This may be due to compatibility issues with the current RT-Thread version. Please refer to the RT-Thread repository for updates.

Spark + RT-Thread

Development Environment

For those unsure where to download the source code, you can refer to the official RT-Thread documentation.

Navigate to the rt-thread\bsp\stm32\stm32f407-rt-spark directory, then open env and enter menuconfig in the command line to enter the configuration interface.

Macro Configuration

Enable the file system (optional):

• Hardware Drivers Config
  • Onboard Peripheral Drivers
    • Enable File System

Enable fatfs (optional):

• RT-Thread Components
  • DFS: device virtual file system
    • Enable elm-chan fatfs
      • elm-chan's FatFs, Generic FAT Filesystem Module
      • Change Maximum sector size to be handled to 4096

Download the mlibc package:

• RT-Thread online packages
  • system packages
    • Select the sixth option from the bottom: mlibc: Embedded libc, especially for RISC-V

After finishing the menuconfig, you need to download the mlibc package before compiling:

# Load the RT-Thread environment
. ~/.env/env.sh

# Update packages to download mlibc
pkgs --update

This will download mlibc to the packages directory.

QEMU-Bare Metal Development

Development Environment

make + qemu + toolchain

Currently, five types of QEMU bare metal startup codes have been supported.

QEMU Device	Hardware Architecture	Toolchain
vexpress-a9	arm	arm-none-eabi-gcc
mps3-an536 (requires latest QEMU)	arm	arm-none-eabi-gcc
virt-aarch64	aarch64	aarch64-unknown-elf-gcc
virt-riscv32	riscv32	riscv32-unknown-elf-gcc
virt-riscv64	riscv64	riscv64-unknown-elf-gcc

Usage Steps

1. Configure the environment variables corresponding to the toolchain

Linux： Add the following environment variables to the ~/.bashrc file through commands. Replace YOUR_PATH_TO_TOOLCHAIN with the corresponding path of your toolchain.

Note: If your toolchain path is "/opt/gcc-arm-none-eabi-10-2020-q4-major/arm-none-eabi-gcc" , then YOUR_PATH_TO_TOOLCHAIN should be "/opt/gcc-arm-none-eabi-10-2020-q4-major/arm-none-eabi-".

echo "" >> ~/.bashrc    #Append a a line break to prevent content merging
echo "export MLIBC_TOOLCHAIN='YOUR_PATH_TO_TOOLCHAIN'" >> ~/.bashrc
source ~/.bashrc

Windows： Open PowerShell and replace YOUR_PATH_TO_TOOLCHAIN with the corresponding path of your toolchain.

[System.Environment]::SetEnvironmentVariable("MLIBC_TOOLCHAIN", "YOUR_PATH_TO_TOOLCHAIN", "User")

#:After the configuration is completed, you need to restart the terminal for the changes to take effect.

2. Navigate to the mlibc root folder and open the command line.

# Here, we use qemu-vexpress-a9 as an example
make qemu-hello QEMU_BOARD=qemu-vexpress-a9 ARCH=arm

After executing the command, an executable file named qemu-vexpress-a9.elf will be generated in the mlibc/build/arm/qemu/qemu-vexpress-a9 folder.

3. Run the script qemu.bat in the corresponding folder under mlibc/helloworld/qemu/{qemu-device}.

# Navigate to the qemu device folder
cd helloworld/qemu/qemu-vexpress-a9

# Enter the following command in the command line
qemu.bat

Information for each virtual environment is as follows:

Filename	Virtual Device	Build Command
qemu-vexpress-a9	vexpress-a9	make qemu-hello QEMU_BOARD=qemu-vexpress-a9 ARCH=arm
qemu-mps3-an536	mps3-an536	make qemu-hello QEMU_BOARD=qemu-mps3-an536 ARCH=arm
qemu-virt-aarch64	virt-aarch64	make qemu-hello QEMU_BOARD=qemu-virt-aarch64 ARCH=aarch64
qemu-virt-riscv32	virt-riscv32	make qemu-hello QEMU_BOARD=qemu-virt-riscv32 ARCH=riscv32
qemu-virt-riscv64	virt-riscv64	make qemu-hello QEMU_BOARD=qemu-virt-riscv64 ARCH=riscv64

Pre-built GCC Toolchains

For convenience, we provide pre-built GCC toolchains with mlibc for multiple architectures. These toolchains are automatically built and released using GitHub Actions.

Downloading Pre-built Toolchains

Visit the Releases page to download pre-built toolchains:

• ARM: arm-linux-eabi_for_x86_64-pc-linux-gnu-*.tar.gz
• RISC-V 32-bit: riscv32-unknown-elf_for_x86_64-pc-linux-gnu-*.tar.gz
• RISC-V 64-bit: riscv64-unknown-elf_for_x86_64-pc-linux-gnu-*.tar.gz
• AArch64: aarch64-linux-gnu_for_x86_64-pc-linux-gnu-*.tar.gz

Installation

# Download and extract
tar -xzf <toolchain-tarball>.tar.gz

# Add to PATH
export PATH=/path/to/toolchain/bin:$PATH

# Verify installation
arm-linux-eabi-gcc --version

Building Toolchains Yourself

If you prefer to build the toolchains yourself:

Using Docker (Recommended)

See toolchain/README.md for detailed instructions on building with Docker.

Using GitHub Actions

The repository includes GitHub Actions workflows for automated builds:

• Build all architectures: Triggered automatically on version tags or manually via workflow dispatch
• Build single architecture: Use the "Build Single Toolchain" workflow for testing

For more information, see .github/workflows/README.md.

License Agreement

mlibc is fully open-source, following the MIT license. It allows for commercial use and modifications without any concerns, provided that the MIT license is declared in the software, with no potential commercial risks.

Contribution

• How to

  1. Fork the repository

  2. Create Feat_xxx branch

  3. Commit your code

  4. Create Pull Request

License

mlibc follows the MIT License free software license. It's completely open-source, can be used in commercial applications for free, does not require the disclosure of code, and has no potential commercial risk.It is only necessary to declare that the MIT protocol is used in the software.